Processing a radio frequency signal

Abstract

Circuitry and a method for use in a radio frequency receiver for processing a radio frequency signal are provided. The circuitry comprises a mixer arranged to receive the radio frequency signal and down-convert the received radio frequency signal to a lower frequency. The received radio frequency signal has an interference component and the interference component in the down-converted signal is within an interference frequency range. The circuitry also comprises an LC based notch filter arranged to receive the down-converted signal from the mixer, filter the down-converted signal, and output the filtered signal for processing by a baseband processing block. The LC based notch filter has a notch centered within said interference frequency range, such that the LC based notch filter is arranged to attenuate the interference component in the down-converted signal.

What is claimed is: 
     
       1. Circuitry for use in a radio frequency receiver for processing a radio frequency signal, the circuitry comprising:
 a mixer arranged to:
 receive the radio frequency signal wherein the received radio frequency signal has an interference component; and 
 down-convert the received radio frequency signal to a lower frequency, wherein the interference component in the down-converted signal is within an interference frequency range; 
 output a differential output signal on two output lines; and 
 
 an LC based notch filter comprising a capacitor, an inductor and a second capacitor arranged in series connecting together the two output lines, arranged to:
 receive the down-converted signal from the mixer; 
 filter the down-converted signal, wherein the LC based notch filter has a notch centered within said interference frequency range, such that the LC based notch filter is arranged to attenuate the interference component in the down-converted signal; and 
 output the filtered signal for processing by a baseband processing block. 
 
 
     
     
       2. The circuitry of  claim 1  wherein the down-converted signal has a desired signal component within a signal frequency range which is distinct from the interference frequency range. 
     
     
       3. The circuitry of  claim 2  wherein the LC based notch filter is configured, based on the output impedance of the mixer and on the capacitive load experienced by the mixer, to have a Q value which is sufficiently high such that the notch filter does not significantly attenuate the desired signal component in the down-converted signal. 
     
     
       4. The circuitry of  claim 1  wherein the LC based notch filter is configured such that the frequency of the notch of the LC based notch filter is adjustable. 
     
     
       5. The circuitry of  claim 1  wherein the LC based notch filter is configured such that the Q value of the LC based notch filter is adjustable. 
     
     
       6. The circuitry of  claim 1  wherein the radio frequency receiver is part of a radio frequency transceiver and wherein the interference component of the received radio frequency signal is caused by a transmitted signal which is transmitted from the radio frequency transceiver. 
     
     
       7. The circuitry of  claim 1  wherein the inductor comprises a powered gyrator and at least one further capacitor is included in the LC based notch filter. 
     
     
       8. The circuitry of  claim 7  wherein the frequency of the notch of the notch filter is adjustable by adjusting one of: the power supplied to the gyrator; and the capacitance of at least one of the at least three capacitors. 
     
     
       9. The circuitry of  claim 7  wherein the LC based notch filter further comprises at least one resistor having an adjustable resistance, and wherein the LC based notch filter is arranged such that the Q value of the LC based notch filter is adjusted by adjusting the resistance of the at least one resistor. 
     
     
       10. The circuitry of  claim 1  wherein the LC based notch filter is configured to have a further notch at a frequency which is within said interference frequency range but which is different to the frequency of said notch. 
     
     
       11. A radio frequency receiver for processing a radio frequency signal, the radio frequency receiver comprising:
 a mixer arranged to:
 receive the radio frequency signal wherein the received radio frequency signal has an interference component; 
 down-convert the received radio frequency signal to a lower frequency, wherein the interference component in the down-converted signal is within an interference frequency range; and 
 output a differential output signal on two output lines; 
 
 an LC based notch filter comprising a capacitor, an inductor and a second capacitor arranged in series connecting together the two output lines, arranged to:
 receive the down-converted signal from the mixer; 
 filter the down-converted signal, wherein the LC based notch filter has a notch centered within said interference frequency range, such that the LC based notch filter is arranged to attenuate the interference component in the down-converted signal; and 
 output the filtered signal; and 
 
 a baseband processing block for processing the filtered signal outputted from the LC based notch filter. 
 
     
     
       12. A method of processing a radio frequency signal in a radio frequency receiver, the method comprising:
 receiving the radio frequency signal at a mixer of the radio frequency receiver, wherein the received radio frequency signal has an interference component; 
 down-converting the received radio frequency signal to a lower frequency using the mixer, wherein the interference component in the down-converted signal is within an interference frequency range; 
 outputting a differential output signal on two output lines; 
 passing the down-converted signal from the mixer to an LC based notch filter of the radio frequency receiver, said LC notch filter comprising a capacitor, an inductor and a second capacitor arranged in series connecting together the two output lines; 
 filtering the down-converted signal with the LC based notch filter, wherein the LC based notch filter has a notch centered within said interference frequency range, such that the LC based notch filter attenuates the interference component in the down-converted signal; and 
 outputting the filtered signal from the LC based notch filter for processing by a baseband processing block. 
 
     
     
       13. The method of  claim 12  further comprising:
 determining the frequency of the interference component in the down-converted signal; and 
 adjusting the frequency of the notch of the LC based notch filter in dependence upon the determined frequency of the interference component. 
 
     
     
       14. The method of  claim 12  further comprising:
 determining the frequency range over which the interference component in the down-converted signal extends; and 
 adjusting the Q value of the LC based notch filter in dependence upon the determined frequency range of the interference component.